Site description Ipassa, also known as Mpassa, is situated in north-east Gabon, west of the town of Makokou. It consists mainly of moist lowland evergreen rainforest, located on a plateau at 450–550 m elevation and drained by small tributaries of the Ivindo river, which forms the southern boundary of the reserve. There are also some areas of mixed swamp-forests in valleys and near streams. Around the headquarters of the reserve’s biological research station, and between it and Makokou, 12 km distant, the vegetation has been much modified and includes extensive fallow and cultivated fields. Rocky islets appear in the Ivindo river during dry seasons.

Key Biodiversity See Box and Tables 2 and 3 for key species. The Ipassa reserve was, for a long time, the most intensely studied forest in Africa. This included about twenty years of ornithological research, during which period 424 species were recorded (not all of which, however, were found in the reserve itself). Three more species have subsequently been observed at Ipassa. Of the four species of global conservation concern known, three are rare migrants—Falco naumanni, Crex crex, and Gallinago media—and, in fact, only recorded from man-made habitats around the reserve. The fourth, Batis minima, is a rare breeding resident. Except for some species restricted to coastal forests or with specific ecological requirements (e.g. Picathartes oreas), the reserve holds almost all forest birds known from Gabon; only 11 species of the Guinea–Congo Forests biome on the Gabon list have not been found at Ipassa.

Non-bird biodiversity: Large mammals Loxodonta africana (EN), Gorilla gorilla (EN) and Pan troglodytes (EN) have been recorded, but their present status is unknown.